The present invention relates to a method and apparatus for folding an airbag for a vehicle occupant restraining system.
U.S. Pat. No. 6,115,998 teaches a method and apparatus for folding an airbag wherein the empty airbag for an airbag module, which is spread out, is gathered together towards a center within a fixed height profile. In contrast to other previously known types of folding, in this method chaotic folding is carried out. Consequently, the folds made have no predetermined shape or direction. Although only a few gathering elements and operational steps are required to gather the airbag together, the chaotic folding may have a negative effect when the airbag module opens. An apparatus for carrying out the method has a lower part for receiving the spread-out airbag and an upper part that is at least in some locations spaced apart from the lower part by gaps. The gaps correspond to the required height profile of the gathered-together airbag. As the gathering elements, slide means are provided between the upper part and the lower part and these surround the airbag at the rim thereof, their position with respect to the latter being variable. The airbag is pushed onto a gas generator of the airbag module, starting from its outer rim and going to the center with the aid of the slide means, and this makes the chaotic folding.
DE 19 751 685 A1 teaches a method and an apparatus for folding an airbag for a vehicle occupant restraining system in which the airbag is folded into an elongate housing. First the airbag is spread out flat on a substrate, and then the wall of the airbag is folded together in a zigzag shape approximately centrally and transversely with respect to the longitudinal direction and is put into the housing. Finally, the end regions of the airbag, starting from the central region put into the housing and progressing towards the ends of the housing, are pressed into the latter. The associated apparatus is has a folding mechanism with a fixed folding part and two movably mounted pushing parts which are displaceable between a position close to the folding part and a position spaced therefrom.
The methods and apparatuses mentioned above have the disadvantage that they are either of complex construction or give only chaotic folding of the airbag in a housing.
The inventive method and apparatus take as their starting point an unfolded airbag that is laid out in a spread-out fashion or is presented with virtually no folds in another way, for example is held hanging.
In the inventive method for folding an airbag, in contrast to the prior art, the airbag is not moved by a gathering element or slide means surrounding the airbag and variable in its position with respect to the latter. Instead, a rotating conveyor element which is mounted to be fixed in its location is used, and this acts on a first portion of the airbag and draws it in the direction of an abutment, at the same time the adjacent second portion being pushed up to the abutment. When conveying using a rotating conveyor element, surprisingly the advantage arises that the spread-out airbag can be moved by means of its first portion in a guided manner in contrast with conventional methods and apparatuses and hence regular and defined folding of the second portion results. The important point is that the airbag to be folded is moved against the abutment, which is substantially fixed in its location, or a stop, during folding.
Whereas with known apparatuses the spread-out airbag is pushed together irregularly at its rim, in accordance with the invention the airbag is drawn by a rotating conveyor element and at the same time is laid in defined manner in folds in a closely delimited space. The rotating conveyor element draws at the spread-out airbag and in so doing smoothes it. Downstream of the conveyor element, the airbag is conveyed against the abutment surface against which it is pushed up. Defined folds are formed, with the airbag advantageously being able to be moved towards the abutment surface at a substantially constant rate of conveying. Whereas with known methods existing folds and regions of different rigidity in the fabric of an airbag have a negative effect on folding, such factors have virtually no effect in the method according to the invention.
Moreover, the method according to the invention can be achieved using relatively simple means, so that, overall, low-cost and at the same time high-quality folding of an airbag for a vehicle occupant restraining system is provided.
The folding made in accordance with the invention can be influenced by the shape of the abutment and the shape and speed of the rotating conveyor element. In this way, chaotic folding can also be made using the inventive method and the apparatus thereof if this is desired.
In the case of an advantageous further development of the invention, the pushed first portion of the spread-out airbag is supported with respect to the rotating conveyor element. Support results in a relatively large abutment force of the first portion of the airbag against the rotating conveyor element. This leads to a relatively large holding force between the airbag and the conveyor element and hence a great pushing action against the first portion. Alternatively, the first portion can lie on the rotating conveyor element and be moved simply on the basis of the holding force produced by its own weight.